The invention relates to an arrangement for damping oscillation of a loading member in a crane comprising a trolley, a hoisting mechanism provided in the trolley, hoisting ropes suspended from the hoisting mechanism, a loading member fastened to the hoisting ropes, the arrangement for damping oscillation of a loading member comprising a vertical guide projection arranged in an upper part of the loading member, and damping members arranged in the trolley and including a guide part receiving the guide projection of the loading member.
Acceleration and deceleration of a crane are mainly responsible for oscillations of a loading member of the crane. This oscillation may be minimized by driving the crane at a constant speed or sufficiently slowly. Research abounds for damping or eliminating oscillations of a loading member of a crane and a load fastened thereto by using various computer programs or speed control methods, e.g. in U.S. Pat. No. 5,219,420. In some cases, particularly in container cranes, oscillation has been suppressed by means of auxiliary ropes and auxiliary drums, cf. for instance U.S. Pat. Nos. 5,769,250 and 7,287,740 as well as DE Patent 1207578. In many applications also pneumatic or hydraulic dampers are used, cf. for instance GB Patent 1542821. However, when using process cranes in connection with heavy loads, such as vacuum hoists including loading members suspended therefrom, the cranes have to be driven at high speeds required by the course of the process. When the commodity to be moved is then e.g. paper or a corresponding product, it is at high risk of being damaged if the liquids used in the crane leak to the product being moved.
U.S. Pat. No. 5,165,556, in turn, describes a device for damping oscillation of a loading member, comprising downward-pointing brackets attached to the bottom of a trolley. A load is lifted in place between these brackets, and the load is retained rigidly in place while driving the crane, whereby oscillation of the loading member and the load attached thereto is prevented. Such damping systems are expensive, and they require a lot of material and space. The damping of this type has a further disadvantage in that when the loading member is lifted at a high speed between the brackets, a gap formed by the brackets for the loading member has to be wide, which may lead to post-oscillations between the brackets. When the loading member has then been supported rigidly between the brackets, accelerations of the trolley directly influence the load attached to the hoisting member. This may lead to malfunction or increased risk of collision, particularly when handling large paper rolls, for instance, when the rolls are kept in place by means of a vacuum hoist.
From JP 08268682 A and KR 20010057393 A, centering of a loading member to a trolley of a crane by means of conical surfaces is known. Therein, a conical loading member centering piece is mounted immovably in the trolley. In the first-mentioned publication, the conical surface of the loading member simultaneously serves as a damper.
DE 10105261 A1 also discloses centering and interlocking means between a loading member and a trolley as well as vertical damping means provided in the trolley for damping a centering event.
In SU 502830 A1, a load is lifted into a tube downwardly extending from a trolley, wherein the load is supported laterally in the tube by means of suspended wheels provided at ends of lever arms.